Del Potro wins twice; Nishikori falls

WASHINGTON – Top seed Juan Martin Del Potro, playing twice in one day for the first time in his career, reached the quarterfinals of the Citi Open with two straight-set triumphs Thursday, but second seed Kei Nishikori — ranked a career-best 11th — could not pull off twin wins at the $1.76 million event.

Del Potro, a two-time Washington champion, dispatched Ryan Harrison 6-1, 7-5 in 70 minutes, then returned five hours later to eliminate No. 14 seed Bernard Tomic 6-3, 6-3 in 69 minutes and advance at the combined ATP and WTA event.

“I feel good,” Del Potro said. “I was training hard before I came here. During the night you feel much better. In the first match, the sun was harder for me. In the night, I move much better.”

Nishikori began the day with a 7-5, 6-2 triumph over wildcard Jack Sock, but was thrashed by 16th-seeded Marcos Baghdatis 6-1, 6-2 in only 58 minutes in his later match.